Ionophores X537A and A23187. Effects on the permeability of lipid bimolecular membranes to dopamine and calcium.

X537A carries dopamine across lipid bimolecular membranes. The rate of transport increases linearly with the X537A concentration and is independent of an electric field across the membrane. The evidence suggests that the permeating species is a neutral 1:1 complex between dopamine and X537A. A23187 does not transport dopamine. The permeability of the membrane to calcium increases as the square of the X537A concentration; the transport of calcium is also increased by A23187. With both ionophores, calcium is probably transported as an uncharged complex. Neither desmethylimipramine nor cocaine alters the transport of dopamine with X537A.